This invention relates to apparatus for detecting incident radiation. More particularly, it is concerned with radiation detecting apparatus employing semiconductor photodiodes.
In conventional semiconductor photodiodes the electric field generated by a rectifying junction is used to separate and to collect the charge carriers (electrons or holes) produced in the semiconductor material by the absorption of incident radiation, specifically energetic particles or photons of light. This action requires that the light be absorbed by the semiconductor material at or near the junction, so that the electrons or holes can diffuse to it and be collected before encountering a recombination center in the semiconductor crystal. In conventional semiconductor photodiodes the junction is parallel to and at a fixed depth below the illuminated surface. Thus, the efficiency of conventional devices varies depending upon the depth of penetration of the radiation with respect to the depth of the junction.